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<title>printf</title>
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<h2 align=center>printf</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
printf - print formatted output
</p>

<h3>Library</h3>
<p>
Standard C Library (libc, -lc)
</p>

<h3>Synopsis</h3>
<p>
<tt>#include &lt;stdio.h&gt;</tt><br>
<br>
<tt>int</tt><br>
<tt>printf(const char *</tt><em>format</em><tt>, ...);</tt>
</p>

<h3>Description</h3>
<p>
<tt>printf</tt> prints formatted text to standard output. The text is
generated from the <em>format</em> argument and subsequent arguments
according to the following rules.
</p>

<p>
Characters in <em>format</em> that are not the percent sign
(<tt>%</tt>) are printed verbatim. When a percent sign is encountered,
the next argument of the arguments following <em>format</em> is
retrieved and printed. The type of the argument expected, as well as
some simple formatting instructions, are derived from the characters
following the percent sign.
</p>

<p>
The following characters designate types to print. One of these
characters concludes the format sequence begun with a percent sign,
and also determines the type expected as an argument.
</p>

<table width=90%>
<tr><td width=5% rowspan=9>
    <td width=5%>%</td>	<td>A percent sign is printed; no argument
				is consumed.</td></tr>
<tr><td>c</td>	<td>Character (char, passed as an integer value)</td></tr>
<tr><td>d</td>	<td>Signed integer value printed in decimal</td></tr>
<tr><td>o</td>	<td>Unsigned integer value printed in octal</td></tr>
<tr><td>p</td>	<td>Pointer (void *)</td></tr>
<tr><td>s</td>	<td>String (const char *)</td></tr>
<tr><td>u</td>	<td>Unsigned integer value printed in decimal</td></tr>
<tr><td>x</td>	<td>Unsigned integer value printed in hexadecimal</td></tr>
<tr><td>X</td>	<td>Unsigned integer value printed in uppercase hex</td></tr>
</table>

<p>
The following characters are modifiers; they can be found between the
percent sign and the type designator.
</p>

<table width=90%>
<tr><td width=5% rowspan=6>
    <td width=5% valign=top>#</td> <td>Select an "alternate
				format". On integer formats this
				causes the C base prefix to be printed
				along with the integer. On other
				formats, this has no effect.</td></tr>
<tr><td valign=top>l</td> <td>Assume an integer argument is
				<tt>long</tt> or <tt>unsigned
				long</tt> instead of <tt>int</tt> or
				<tt>unsigned int</tt>. If repeated,
				the argument is taken to be <tt>long
				long</tt> or <tt>unsigned long
				long</tt>. </td></tr>
<tr><td valign=top>z</td> <td>Assume an integer argument is
				<tt>ssize_t</tt> or <tt>size_t</tt>
				instead of <tt>int</tt> or
				<tt>unsigned int</tt>. </td></tr>
<tr><td valign=top>0-9</td> <td>Digits are treated as a decimal number,
				which is considered to be the field
				width. The argument is printed
				right-aligned in a field that many
				characters wide.</td></tr>
<tr><td valign=top>0</td> <td>If the field width has a leading 0, the
				padding character for alignment is
				made 0 (zero) instead of
				space.</td></tr>
<tr><td valign=top>-</td> <td>If a field width is given, use it for
				left alignment instead of right
				alignment.</td></tr>
</table>

<h3>Restrictions</h3>
<p>
Note that this is a limited printf implementation - it has no support
for precisions (".number" as a modifier), floating-point formats,
field widths passed as arguments, or the rarely-used plus and space
modifiers.
</p>

<h3>Return Values</h3>
<p>
<tt>printf</tt> returns the number of characters printed.
</p>

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